This invention relates generally to a gearshift lever for automatic transmissions and more particularly to a locking device for gearshift levers that are moved through a series of positions to effect different operating and drive conditions of the transmission.
A problem occurring in automobiles with automatic transmissions is the inadvertent movement of the car resulting from a driver changing the gearshift lever from the park position to a drive position while inadvertently stepping on the gas pedal rather than the intended action of stepping on the brake pedal. It is thus desirable to provide a lockable gearshift lever in automatic transmissions that require the driver to keep his foot on the brake pedal in order to move the gearshift lever from the park position and into a driving position.
In addition to controlling movement of the gearshift lever out of the park position when the ignition is on and the motor is running, it is also desirable to control movement of the gearshift lever when the ignition is off. Even if the motor is not running the car may move forward or backward if it is on an inclined surface when the gearshift lever is moved out of the park position. One method for locking the gearshift lever is to provide an electrically activated locking device that locks the lever in response to a continuous electrical signal. However, such method is not effective when the ignition is off because the electrical power of the battery is insufficient to meet the power consumption needs of the electrical locking device.
Another possible solution to the proposed problem is to electrically connect the locking device such that in an electrically excited condition the locking device releases the gearshift lever, while in an unexcited condition the gearshift lever remains blocked. This ensures that, when the ignition is off, the gearshift lever remains locked in the park position. The locking device can become electrically operable to release the gearshift lever only when the ignition is turned on and the brake pedal is depressed. This proposed solution provides a disadvantage in that the lock must be electrically powered in an unlocked position during the entire period that the car is being operated. Further, the mechanical locking devices previously suggested have been subject to wear on the bolts connecting the locking device since the locking device is engaged for a substantial amount of time (i.e. while the car is not running).
It is therefore an object of the present invention to provide a locking device for the gearshift lever of an automatic transmission that effectively locks the gearshift lever in the park position, that consumes a minimum of electric current, and that does not release the gearshift lever from the park position even when the ignition is shut off. In summary, the present invention provides a switch that is activated when an attempt is made to move the gearshift lever from neutral in the park position into one of the drive positions. The switch detects the initial movement of the gearshift lever and activates the locking device unless certain other criteria are met. The locking device, thus activated, securely holds the gearshift lever in the park position preventing its movement into one of the drive positions. The present invention places a negligible load on the capacity of the battery by ensuring that current flow occurs only during the time in which an attempt is made to move the gearshift lever out of the park position.